1. Field of the Invention
The invention relates to a method and a circuit for black level setting, and to a display apparatus including a black level setting circuit.
2. Description of the Related Art
U.S. Pat. No. 5,278,476 (PHN 13,885), incorporated by reference herein, discloses a display apparatus including a black level setting circuit with a control circuit adapted to successively apply at least two control voltages, in a predetermined ratio, to the cathode of the display device. Moreover, the black level setting circuit includes a correction circuit for supplying a correction value dependent on the ratio between the currents generated in the relevant cathode in response to the at least two control voltages. The following formula is given for the cathode current Ik: EQU Ik=(K*Vd)/Vco.sup.(1-1.5/.gamma.) !.sup..gamma.
where Vd is the drive voltage, Vco is the cut-off voltage, and .gamma. (gamma) is a quantity related to the display tube. In one embodiment, a multiplier circuit provides a gain control to ensure that an arbitrary video voltage applied to the input yields the same cathode current for all three electron guns (cathodes), provided that the factors K and .gamma. are equal for all three cathodes.